A conventional acceleration sensor often takes the form of a capacitive acceleration sensor. The seismic mass of the capacitive acceleration sensor may be formed as an antisymmetric rocker. A micromechanical acceleration sensor having a seismic mass in the form of an antisymmetric rocker is described, for example, in European Patent Application Publication EP 0 773 443 A1.
Seismic masses in the form of rockers are also used for sensors to determine a tilt angle of a vehicle. A sensor of that kind for determining a tilt angle of a vehicle is described, for example, in European Patent Application Publication EP 0 244 581 A1.
FIGS. 1A to 1C show, respectively, one cross-section and two plan views to illustrate a conventional acceleration sensor.
The capacitive acceleration sensor shown in cross-section in FIG. 1A is designed to detect an acceleration of the acceleration sensor oriented in a direction perpendicular to a wafer 10 (z-direction), and to determine a quantity corresponding to the acceleration. To that end, a seismic mass 12 formed as an antisymmetric rocker is adjustably disposed above wafer 10. Seismic mass 12 is joined via two torsion springs 14 (see FIG. 1B) to an anchoring 16, which is fixedly disposed on wafer 10. Torsion springs 14, not shown in FIG. 1A, extend along a longitudinal axis 18, around which seismic mass 12 in the form of a rocker is adjustable.
Seismic mass 12 includes a first electrode 20a situated on a first side of longitudinal axis 18, and a second electrode 20bsituated on the second side of longitudinal axis 18. Because of an additional mass 22, second electrode 20b may have a larger mass than first electrode 20a. 
Counter-electrodes 24a and 24b to electrodes 20a and 20b of seismic mass 12 are applied fixedly on wafer 10. The sensor principle of the acceleration sensor is thus based on a spring-mass system, in which movable seismic mass 12, together with counter-electrodes 24a and 24b fixed in position on wafer 10, form two plate-type capacitors. In this context, counter-electrodes 24a and 24b, shown in plan view in FIG. 1C, are disposed in such a way in relation to electrodes 20a and 20bthat the position of seismic mass 12 relative to wafer 10 is ascertainable by evaluation of a first capacitance between electrode 20a and associated first counter-electrode 24a and a second capacitance between electrode 20b and associated second counter-electrode 24b. 
FIG. 2 shows a cross-section through the conventional acceleration sensor of FIGS. 1A to 1C to illustrate its mode of operation.
If, as shown in FIG. 2, the acceleration sensor experiences an acceleration 26 in the z-direction, then, because of additional mass 22, a force aimed in the direction of wafer 10 acts on second electrode 20b. Therefore, due to acceleration 26, seismic mass 12 in the form of a rocker is moved around the longitudinal axis (not sketched) in such a way that a first average distance dl between first electrode 20a and first counter-electrode 24a increases, and a second average distance d2 between second electrode 20b and second counter-electrode 24b decreases.
The changes in the capacitances of the two capacitors, formed of electrodes 20a and 20b and counter-electrodes 24a and 24b, which correspond to the changes in distances d1 and d2, may subsequently be evaluated to determine acceleration 26. Since methods for evaluating changes in capacitance are known from the related art, they are not further discussed here.
FIG. 3 shows a cross-section through the conventional acceleration sensor of FIGS. 1A to 1C in the context of a mechanical stress exerted on the acceleration sensor.
In FIG. 3, a mechanical stress is acting upon wafer 10, by which wafer 10 is bent asymmetrically along the y-axis. For example, first average distance dl between first electrode 20aand first counter-electrode 24a changes due to the asymmetrical bending of wafer 10. In the same way, second average distance d2 between second electrode 20b and second counter-electrode 24b may increase or decrease under the influence of a mechanical stress.
Thus, in the case of the conventional acceleration sensor, a mechanical stress, which, for example, is produced via a force or via a pressure on at least one part of the acceleration sensor, particularly on a subunit of the housing, is able to bring about a change in the capacitance of the capacitors made up of electrodes 20a and 20b and counter-electrodes 24a and 24b. As a rule, an evaluation unit (not shown) of the acceleration sensor is unable to distinguish the change in capacitance caused by an influence of stress from a change in capacitance triggered by an acceleration of the acceleration sensor. As a result, the acceleration sensor interprets a mechanical stress as an acceleration, and outputs a corresponding false message. This is also referred to as an offset of the measured acceleration caused by an influence on the housing.
It is desirable to have the possibility of operating an acceleration sensor in which the acceleration sensor is relatively insensitive to a mechanical stress exerted on the acceleration sensor.